Split thread orthopaedic implant impactor

ABSTRACT

A method of connecting an impactor to an orthopaedic implant includes the steps of: providing the impactor including a shaft having a proximal end and a distal end, a trigger pivotably connected to the distal end, the trigger including a cam end, a push rod within the shaft and connected to the cam end of the trigger and a threaded pair connected to an end of the push rod opposite the trigger; providing the orthopaedic implant including a threaded hole; locating the threaded pair within the threaded hole; pivoting the trigger; linearly displacing the push rod; and radially expanding the threaded pair to engage the threaded hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 11/339,130,entitled “SPLIT THREAD ORTHOPAEDIC IMPLANT IMPACTOR”, filed Jan. 25,2006, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to orthopaedic instruments, and, moreparticularly, to orthopaedic implant impactors.

2. Description of the Related Art

The hip joint is configured as a ball and socket arrangement whichincludes the femoral head joined to the natural socket or acetabulumlocated in the pelvis. Deterioration of the acetabulum and/or femoralhead can be brought about by injury or progressive diseases such asosteoarthritis. When injury or disease occurs, the damaged component(s)can be replaced or rebuilt using appropriate orthopaedic implants. Inthe technique known as a “total hip replacement”, one method involvescementing or press-fitting an acetabular cup prosthesis into theacetabulum after the acetabulum has been sufficiently reamed to acceptthe cup. Additionally, fixation fasteners can be used to hold the cup inthe acetabulum, and the cup can include a porous coating on the convexside to promote bone ingrowth. The femoral head can also typically bereplaced.

In order to properly seat an acetabular cup into the acetabulum animpaction tool, or impactor, is used by the surgeon to firmly seat thecup. The impactor needs to securely hold the cup while the cup is beinglocated in the acetabulum, and the impactor also needs to securely holdthe cup while the cup is being impacted into the acetabulum. Theacetabular cup impactor can include a surgical implement coupler whichcan be secured to the acetabular cup. An elongated shaft is joined tothe surgical implement coupler at one end, and includes a striker cap atthe opposite end of the shaft. The cup is seated in the preparedacetabulum by positioning the cup in the prepared depression, andimparting a series of blows from a mallet against the striker cap. Theforce of the blows is transmitted through the shaft of the impactor, toseat the cup in the prepared opening in the acetabulum. After the cup isproperly seated, the surgical implement coupler of the impactor isdetached from the cup.

Particularly in a minimally invasive procedure, where a small incisionis made to reduce the trauma to surrounding tissue, at least twoproblems occur in seating an acetabular cup. It is difficult to properlyalign the impactor because of anatomical features that are in the way,and disconnecting the head from the cup is more difficult with limitedaccess to the end of the tool. Cleaning and sterilization of theimpactor after surgery can also be difficult.

An acetabular cup impactor is known with a curved shaft that makesproper alignment of the tool more easily accomplished during a minimallyinvasive surgical procedure, and includes a remotely activated surgicalimplement coupler for disengaging the head from an acetabular cup. Thesurgical implement coupler is adapted for selective attachment to anddetachment from an orthopedic device such as an acetabular cup. Thesurgical implement coupler includes a threaded stud rotatably disposedin and retained by a sleeve. The threaded stud is adapted for threadedengagement with an acetabular cup or other orthopedic device. Auniversal joint or swivel drive is disposed rotatably in the shaftassembly and is drivingly connected to the threaded stud such thatrotation of the swivel drive causes rotation of the threaded stud in thesleeve. A thumb wheel near the handle of the impactor actuates theswivel drive. A problem with this design is that it requires thethreaded stud to be threaded into the acetabular cup, and this threadingprocess can be tedious and time consuming, and can result incrossthreading the threaded stud into the acetabular cup with aresultant less than secure connection between the threaded stud and theacetabular cup. Another problem with this design is that it issubstantially closed along the shaft which makes the internalcomponents, such as the swivel drive, difficult to clean and sterilize.

An acetabular cup impactor or inserter is known with a curved shaft andwhich encloses a drive train and which includes at a far end, aprosthesis (acetabular cup, for example) engaging collet, and at theopposite end, a knob or handle which facilitates turning of the drivetrain by the operator. When knob is turned in one direction, theprosthesis-engaging collet locks the prosthesis against rotationalmovement. Further, the collet action eliminates the need of threadingthe acetabular prosthesis on the end of the inserter as the prosthesiscan simply be placed over the collet and the collet expanded so as togrip the internal threads of the prosthesis. Turning the knob in theopposite direction can release the collet from the prosthesis. Althoughthis design eliminates the need to thread the collet into the cup, theknob is relatively far from the impactor handle, and because of therotational movement required by the knob, releasing the cup from theimpactor is a two handed operation. Further, it is largely a closeddesign which makes the drive train difficult to clean and sterilize.

What is needed in the art is an orthopaedic implant impactor which iseasy to use in a minimally invasive procedure, which can engage andrelease a prosthesis with a simple motion and which is easy to clean.

SUMMARY OF THE INVENTION

The present invention provides an orthopaedic impactor with a push rodlinearly displaceable within an open shaft, where the push rod isactuated within the shaft by a trigger to engage and release an implant.

The invention comprises, in one form thereof, an orthopaedic implantimpactor which includes a shaft having a proximal end and a distal end.A trigger is pivotably connected to the distal end, the trigger having acam end. A push rod is within the shaft and is connected to the cam endof the trigger.

The invention comprises, in another form thereof, an orthopaedic implantimpactor which includes a trigger having a cam end and a push rodconnected to the cam end of the trigger. A shaft includes a proximal endand a distal end, and the push rod extends substantially from theproximal end to the distal end. The shaft includes an aperture exposingthe push rod along a substantial length of the push rod.

The invention comprises, in another form thereof, a method of connectingan impactor to an orthopaedic implant, including the steps of: providingthe impactor including a shaft having a proximal end and a distal end, atrigger pivotably connected to the distal end, the trigger including acam end, a push rod within the shaft and connected to the cam end of thetrigger, and a threaded pair connected to an end of the push rodopposite the trigger; providing the orthopaedic implant including athreaded hole; locating the threaded pair within the threaded hole;rotating the trigger; linearly displacing the push rod; and radiallyexpanding the threaded pair to engage the threaded hole.

An advantage of the present invention is that it is easy to use in aminimally invasive surgical procedure.

Another advantage of the present invention is that it is time efficientfor the surgeon to use, particularly with respect to engaging anddisengaging the acetabular cup.

Yet another advantage of the present invention is that it is easy toclean and sterilize.

Yet another advantage of the present invention is that the impactioncollar subassembly is easily removed from the impactor.

Yet another advantage of the present invention is that the impactioncollar subassembly is easily installed onto the impactor.

Yet another advantage of the present invention is that the impactioncollar subassembly can be compatible with many different manufacturer'sstyles of acetabular cups.

Yet another advantage of the present invention is that impactor can beeasily configured for a particular manufacturer's style of acetabularcup by simply installing the appropriate impaction collar subassembly.

Yet another advantage of the present invention is that manufacturingefficiencies are achieved in that the components of the impaction collarsubassembly are interchangeable, and a variety of impaction collarsubassemblies can be used with a single impaction tool subassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a perspective view of an embodiment of an orthopaedic implantimpactor according to the present invention, shown in relation to anembodiment of a disengaged acetabular cup prosthesis;

FIG. 2 is a top view of the impactor of FIG. 1;

FIG. 3 is a side view of the impactor of FIG. 1;

FIG. 4 is a cross-sectional view of the impactor of FIG. 1 taken alongsection line 4-4 in FIG. 2;

FIG. 5 is a fragmentary perspective end view of the impactor of FIG. 1,shown with the impaction collar subassembly removed;

FIG. 6 is a fragmentary cross-sectional side view of the end of theimpactor of FIG. 1, shown with the impaction collar subassembly prior toassembly onto the end of the impactor;

FIG. 7 is a a fragmentary perspective view of the impactor of FIG. 1,shown with the impaction collar subassembly partially exploded;

FIG. 8 is an end view of the acetabular cup prosthesis of FIG. 1;

FIG. 9 is a cross-sectional view of the acetabular cup of FIG. 1 takenalong section line 9-9 in FIG. 8;

FIG. 10 is a fragmentary side view of the impactor and acetabular cup ofFIG. 1, shown prior to engaging the cup with the impactor;

FIG. 11 is a fragmentary side view of the impactor and acetabular cup ofFIG. 1, shown after engaging the cup with the impactor;

FIG. 12 is a fragmentary cross-sectional view of the impactor of FIG. 1,showing particularly the impaction collar subassembly connected to theend of the impaction tool subassembly, and shown prior to engaging thecup with the impactor;

FIG. 13 is a fragmentary cross-sectional view of the impactor of FIG.12, shown engaging the cup with the impactor;

FIG. 14 is a fragmentary cross-sectional view of the impactor/acetabularcup combination of FIG. 13, shown prior to engaging the cup in aprepared acetabulum;

FIG. 15 is a fragmentary cross-sectional view of the impactor/acetabularcup combination of FIG. 13, shown setting the cup in a preparedacetabulum;

FIG. 16 is a side view of the impactor/acetabular cup combination ofFIG. 13, shown impacting the cup in a prepared acetabulum; and

FIG. 17 is a fragmentary cross-sectional view of the impactor/acetabularcup combination of FIG. 13, shown after setting/impacting the cup in aprepared acetabulum, and after disengaging the cup with the impactor.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplifications are not to be construed as limiting the scope ofthe invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown an orthopaedic implant impactor 20 and an orthopaedic implant 21shown as an acetabular cup prosthesis.

Shown more particularly in FIGS. 2-6, impactor 20 includes impactiontool subassembly 22 and impaction collar subassembly 24. Impaction toolsubassembly 22 includes handle subassembly 26 connected to impactorshaft 28. Handle subassembly 26 includes a handle 29, a strikecap 30connected to handle shaft 32, and handle shaft 32 can be fixedlyconnected to impactor shaft 28 using pin 34. Impaction tool subassembly22 further includes alignment guide subassembly 36 which is rotatablearound handle shaft 32, and which can be fixed in place by tighteningalignment guide lock nut 38 against washer 40 and alignment guidesubassembly 36. Push rod 42 and cam lock lever or trigger 44 are bothconnected to distal end 46 of impactor shaft 28 at pins 48 and 50,respectively. Push rod 42 is biased against trigger 44 by resilientmember 52, which is shown as a spring, at proximal end 54 of impactorshaft 28. Cam lock lever 44 is pivotably connected to distal end 46 atpin 50, and includes a cam end 56 connected to push rod 42. Push rod 42includes slot 58 which is connected to pin 48 so that push rod 42 islinearly displaceable along shaft 28 when trigger 44 is rotated.Impaction tool subassembly 22 further includes a shaft collar 60, and arelease button 62 connected to a release pin 64, where both releasebutton 62 and release pin 64 are biased toward the end of shaft collar60 with a resilient member such as spring 66. J-slots 68, along withrelease button 62, release pin 64 and spring 66, facilitate a relativelyeasy removal and fixation of impaction collar subassembly 24 relative toimpaction tool subassembly 22, as will be discussed further below. Pushrod 42 extends substantially from proximal end 54 to distal end 46, andimpactor shaft 28 includes at least one aperture 70 exposing push rod 42along a substantial length of push rod 42, which allows impactor 20 toat least be easily cleaned, sterilized and maintained. Push rod 42extends into aperture 72 of shaft collar 60.

Impaction collar subassembly 24 (see particularly FIGS. 4, 6 and 7) isconnected to push rod 42 and shaft collar 60. Impaction collarsubassembly 24 includes a threaded pair 74 held together with an O-ring76 and a wedge 78 inserted between threaded pair 74. Impaction collarsubassembly 24 further includes a sleeve 80 and an impaction collar 82,where threaded pair 74, O-ring 76 and wedge 78 are held at leastpartially within impaction collar 82. Wedge 78 includes a first wedgeface 84 and a second wedge face 86 and a slot 88 extending from firstwedge face 84 to second wedge face 86. A pin 90 is inserted through slot88 and connected to impaction collar 82. Threaded pair 74 includes afirst half 92 with a first wedge end 94 which has a first hole 96 and asecond half 98 with a second wedge end 100 which has a second hole 102,and pin 90 is also inserted through first hole 96 and second hole 102.Consequently, both wedge 78 and threaded pair 74 are constrained by pin90 relative to impaction collar 82. That is, wedge 78 can movelongitudinally, but not radially, relative to impaction collar 82;whereas each of first half 92 and second half 98 of threaded pair 74 canmove radially, but not longitudinally, relative to impaction collar 82.

FIGS. 8 and 9 illustrate an embodiment of acetabular cup prosthesis 21.The size and geometry of acetabular cup prosthesis 21 can vary frommanufacturer to another manufacturer, and can also vary from productline to another product line of a given manufacture. The size andgeometry of acetabular cup prosthesis 21 also is dictated by the patientwhose hip is being replaced. Cup 21 may be porous coated on their convexside to promote bone ingrowth, and may provide some method to firmlyattach a poly liner which can vary among manufacturers and/or productlines. Cup 21 can include fixation screw through holes 104 foracetabular fixation screws, and the presence, size, number and locationof holes 104 can vary among manufacturers and/or product lines. Threadedhole 106, which may or may not be a through hole, is used to connectimpactor 20 with implant 21. The size (for example diameter and depth)and thread type (for example threads/unit length and thread standard) ofthreaded hole 106 can vary among manufacturers and/or product linesand/or sizes of implant 21.

As shown particularly in FIGS. 10-13, when cam lock lever 44 is pivotedand linearly displaces push rod 42, push rod 42 presses against wedge 78to move wedge 78 towards the longitudinally fixed threaded pair 74, andradially expands first half 92 and second half 98 against O-ring 76.When threaded pair 74 is within threaded hole 106 of implant 21, andthreaded pair 74 is actuated to radially expand within threaded hole106, threaded pair 74 engages threaded hole 106 (FIG. 13), by engagingfirst threaded end 116 and second threaded end 118 into the threads ofthreaded hole 106, and thereby allows a surgeon to position and impactacetabular cup 21 into a prepared acetabulum 108 using impactor 20(FIGS. 14-16). A reverse motion of trigger 44 radially retracts firsthalf 92 and second half 98 to disengage threaded pair 74 from threadedhole 106 and thereby release impactor 20 from acetabular cup 21.

As previously discussed, the size and thread type of threaded hole 106varies. Consequently, the size and thread type of threaded pair 74(first threaded end 116 and second threaded end 118) can be varied to becompatible with different implants 21. Installing a different threadedpair 74 into impaction collar subassembly 24 can be tedious and timeconsuming, and generally not suitable for a surgical environment and/orsurgical procedure. Instead, the present invention allows for quickattachment and detachment of impaction tool subassembly 22 fromimpaction collar subassembly 24, and a variety of impaction collarsubassemblies 24 can be available, each with a different threaded pair74 to accommodate the different threaded holes 106 (size and threadtype) of different implants 21. When impaction collar subassembly 24 isslid over shaft collar 82, the base of impaction collar 82 depressesrelease pin 64, and locking pins 110, 112 are inserted into J-slots 68.Impaction collar subassembly 24 is then rotated relative to shaft collar82, locking pins 110, 112 continue into J-slots 68, and release pin 64is biased into release pin hole 114 of impaction collar subassembly 24,thereby locking impaction collar subassembly 24 relative to impactiontool subassembly 22. To release impaction collar subassembly 24 fromimpaction tool subassembly 22, release button 62 is depressed away fromimpaction collar subassembly 24, thereby releasing release pin 64 fromrelease pin hole 114, and impaction collar subassembly 24 is rotated andthen translated to release locking pins 110, 112 from J-slots 68 therebyfreeing impaction collar subassembly 24 from impaction tool subassembly22. In this way a variety of impaction collar subassemblies 24 can beavailable during surgery, or in a surgical tool kit, each having adifferent threaded pair 74 corresponding to a different type of implant21. Once an implant 21 is selected, a corresponding impaction collarsubassembly 24 can be easily and quickly installed onto impactor 20.Additionally, manufacturing efficiencies are achieved by the presentinvention in that the components of impaction collar subassembly 24 areinterchangeable, and a variety of impaction collar subassemblies 24 canbe used with a single impaction tool subassembly 22.

In use, the present invention provides a method of connecting animpactor 20 to an orthopaedic implant 21, including the steps of:providing impactor 20 including a shaft 28 having a proximal end 54 anda distal end 46, a trigger 44 pivotably connected to distal end 46,trigger 44 including a cam end 56, a push rod 42 within shaft 28 andconnected to cam end 56 of trigger 44, and a threaded pair 74 connectedto an end of push rod 42 opposite trigger 44; providing orthopaedicimplant 21 including a threaded hole 106; locating threaded pair 74within threaded hole 106; pivoting trigger 44; linearly displacing pushrod 42; and radially expanding threaded pair 74 to engage threaded hole106.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. A method of connecting an impactor to an orthopaedic implant,comprising the steps of: providing said impactor including a shafthaving a proximal end and a distal end, a trigger pivotably connected tosaid distal end, said trigger including a cam end, a push rod withinsaid shaft and connected to said cam end of said trigger and a threadedpair connected to an end of said push rod opposite said trigger;providing the orthopaedic implant including a threaded hole; locatingsaid threaded pair within said threaded hole; pivoting said trigger;linearly displacing said push rod; and radially expanding said threadedpair to engage said threaded hole.
 2. The method of claim 1, furthercomprising the step of linearly displacing said wedge by said push rodand thereby selectively moving said threaded pair between an openposition and a closed position.